The term 'established rule' can be summarized by two crossword solutions: AXIOM and rubric. An AXIOM is a self-evident truth or a statement that is accepted as true without proof. It is a fundamental principle that serves as the basis for a system of belief or behavior. A rubric is a set of criteria used to evaluate performance, usually in the form of a chart or grid. It is a guide that outlines what is expected in terms of quality and performance, and it is often used to grade student work. Both axioms and rubrics are established rules that provide guidance and structure.